In oil and gas production wells, scale formation is a significant issue. As used herein, the term “scale” refers to deposits or coatings formed on borehole tubulars and components. Produced water includes formation water that is often saturated with mineral ions. During well operation, formation water may mix with water from other zones, injected water from injection wells, or other injected materials that may have different ionic species. This mixing of incompatible water, along with changes in temperature or pressure, often results in the development of scale. Common scales include calcium carbonate, calcium sulfate, barium sulfate, strontium sulfate, iron sulfide, zinc sulfide, iron carbonate, iron oxides, and barium strontium sulfate. Scale builds up on the surfaces of borehole tubulars and/or components in contact with produced water, impeding fluid flow. If no countermeasures are taken, the borehole tubulars and/or components may become completely blocked over time.
Corrosion is also a large concern in oil and gas production wells. As used herein, the term “corrosion” refers to a loss of metal due to chemical or electrochemical reactions. Borehole tubulars and components are typically made of steel, an alloy consisting mostly of iron. When iron is in contact with water containing dissolved oxygen, sulfur dioxide, and/or carbon dioxide, iron hydroxide species can form on the surface of the iron. Similarly, when iron is in contact with water containing dissolved carbon dioxide and hydrogen sulfide, iron sulfide species can form on the iron surface. As the iron hydroxide or iron sulfide species flake off from the surface, fresh iron is exposed. This corrosion process continues until either all of the iron is consumed, or until one of the reactant species is removed or consumed. Corrosion products that accumulate such as iron hydroxide and iron sulfide may also be considered as scale.
Inhibitors are often periodically circulated through the various flow paths of a well to prevent or reduce scaling and/or corrosion. However, such inhibitors are often unnecessary or are overused as a precautionary measure due to a lack of knowledge about the precise conditions downhole.
While the invention is susceptible to various alternative forms, equivalents, and modifications, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto do not limit the disclosure, but on the contrary, they provide the foundation for alternative forms, equivalents, and modifications falling within the scope of the appended claims.